Primary 4 Science Semestral Assessment 2 (End of Year) Paper 3

TuitionGoWhere Practice Paper - Science Primary 4

SA2 End-of-Year Examination - Version 3 of 5

ANSWER KEY

SECTION A: MULTIPLE CHOICE [15 marks]

SECTION B: SHORT ANSWER [25 marks]

16(a) P and R [1]

Leaves P and R both show net-like (reticulate) vein patterns where veins branch and interconnect across the leaf blade.

16(b) Grasses / Maize / Corn / Rice / Wheat / Bamboo / Any monocot plant [1]

These are monocot plants characterized by parallel-veined leaves. Dicots generally have net-like veins.

16(c) P and R (or: the plants with net-like veins) [1]

Explanation: Flowering plants (dicotyledons) usually have net-like veins in their leaves. Net-like veins help to support the leaf and transport water and food throughout the broad leaf surface. Plants with parallel veins are typically monocots, which are also flowering plants, but the more common P4 syllabus association is that dicots = net-like veins = flowering plants. The presence of net veins is a key identifying feature of dicot flowering plants. [1]

Marking note: Accept either P/R or acknowledge that both P/R and Q/S could be flowering plants, but net-like veins specifically indicate dicots. Full marks for identifying P/R with correct reasoning.

17(a) Animal T [1]

Fish have scales, breathe through gills, and have no legs (they have fins for swimming).

17(b) Bird [1]

Feathers are unique to birds. Birds breathe with lungs, have two legs (wings are modified forelimbs), and are warm-blooded vertebrates.

17(c) Any one of: [1]

• It has moist skin (reptiles have dry, scaly skin)
• It breathes through its skin as well as lungs (reptiles only use lungs)
• It does not have scales (reptiles have scales)

Marking note: Any valid distinction between amphibian and reptile characteristics is accepted.

17(d) Any one of: [1]

• It has fur/hair
• It feeds its young with milk
• It is warm-blooded
• It has external ear flaps (pinnae)

18(a) Wind dispersal [1]

The spinning winged structure (samaras) helps the seed float through the air.

18(b) Any two of: [2]

• The seed/fruit has a fibrous husk [1] that contains air spaces, making it light and able to float [1]
• The husk is waterproof/protects the seed from getting wet [1]
• It is round and can roll/flow easily with water currents [1]

18(c) Any two of: [2]

• To prevent overcrowding so seedlings have space, light, and nutrients to grow [1]
• To reduce competition with the parent plant for water, sunlight, and minerals [1]
• To allow the species to colonize new habitats/survive in different conditions [1]

19(a) Y (cardboard) [1]

Cardboard does not allow any light to pass through — it is opaque.

19(b) W and Z [1] (or: clear glass and clear plastic)

Both clear glass and clear plastic are transparent — light passes through them directly without being scattered.

19(c) Translucent (material) [1]

Translucent materials allow some light to pass through but scatter it, so objects cannot be seen clearly through them. Frosted glass diffuses light.

20(a) Evaporation [1]

Heat from the sun causes water from the sea/river to change into water vapour (gas) and rise into the air.

20(b) Condensation [1]

Water vapour in the air cools down and changes back into tiny water droplets (liquid) around dust particles. These droplets join together to form clouds. When they become too heavy, they fall as rain.

20(c) Any two of: [2]

• It provides freshwater for drinking and daily use [1]
• It provides water for plants to grow, which produce food and oxygen [1]
• It maintains the balance of water in the environment [1]
• It helps in weathering and shaping the land [1]

21(a) Gas [1]

Gas particles have the most energy — they move freely and rapidly in all directions, filling the space available.

21(b) Any two of: [2]

• The particles gain energy from the heat [1]
• The particles move faster and vibrate more vigorously [1]
• The arrangement becomes less ordered/more random [1]
• The particles are able to slide past each other rather than being fixed in position [1]
• Spaces between particles increase slightly [1]

Key concept: In melting, the particles gain enough energy to overcome the forces holding them in fixed positions, but not enough to break free completely (which would be boiling/evaporation).

22(a) Incomplete [1]

Grasshoppers develop through egg → nymph → adult without a pupal stage. The nymph resembles a small adult.

22(b) Three [1]

Egg → Tadpole → Adult (or: Egg → Tadpole → Froglet → Adult — accept three main stages or four if froglet is included)

22(c) Any one valid comparison with explanation: [2]

• The frog has complete metamorphosis while the grasshopper has incomplete metamorphosis [1] — the frog has a pupa/tadpole stage where it looks very different from the adult, but the grasshopper's nymph looks similar to the adult [1]
• The frog's young lives in water and breathes with gills, while the adult lives on land and breathes with lungs [1] — the grasshopper breathes with air throughout its life using spiracles/tracheae [1]
• The frog develops through radical body changes (losing tail, growing legs, developing lungs), while the grasshopper mainly grows larger and develops wings [1]

SECTION C: STRUCTURED RESPONSE [20 marks]

23(a)

[2 marks: 1 mark for correct plants; 1 mark for correct animals — deduct 0.5 for each error, minimum 0 per column]

23(b) Any two valid changes with explanations: [4]

• Develops legs: The tadpole grows hind legs first, then front legs [1] to help it move on land when it becomes a frog [1]
• Loses tail: The tail shrinks and is absorbed into the body [1] as it is no longer needed for swimming [1]
• Develops lungs: The tadpole breathes with gills in water [1] but develops lungs to breathe air on land [1]
• Changes diet: Tadpoles are herbivores (eat algae/plants) [1] but adult frogs are carnivores (eat insects) [1]

Marking note: Each change must include what changes AND why/how this helps survival. Award [1] for identifying change, [1] for explaining significance.

23(c) Flowering plants / Angiosperms [1]

Explanation: The water lily produces flowers, which is the defining feature of flowering plants (angiosperms). Flowers are the reproductive structures that develop into fruits containing seeds. [1]

24(a) To compare with/To act as a control/To show what happens without any wrapping [1]

The control cup allows Sarah to compare whether the wrapping materials actually make a difference to temperature change.

24(b) Plastic foam (Cup D) [1]

Explanation: It has the lowest temperature after 30 minutes (18°C), meaning least heat entered the drink [1]. The temperature rose by only 3°C from a typical cold starting point (assumed 15°C), or stayed coolest compared to others, showing it best prevented heat transfer from surroundings. [1]

Alternative: If assuming all started at same cold temperature, D is clearly coolest, meaning least heat gained.

24(c) Disagree [1]

Evidence: Aluminium foil (a metal, good conductor) gave temperature 24°C, close to unwrapped cup [1] — poor insulation. Cotton and plastic foam (poor conductors, good insulators) kept drink colder. A good conductor allows heat through easily, so it is a poor insulator. The results show conductors and insulators have opposite effects. [1]

24(d) Any one valid improvement: [1]

• Repeat the experiment several times and calculate average temperatures
• Use a thermometer with finer scale/more precise readings
• Ensure all drinks start at exactly the same temperature
• Use same thickness of each wrapping material
• Conduct experiment in a temperature-controlled room
• Place cups the same distance from heat sources

25(a) Grass [1]

Producers are organisms that can make their own food through photosynthesis. Plants are producers.

25(b) The direction of energy flow / "The caterpillar eats the grass" / Energy transfer from grass to caterpillar [1]

Arrows in food chains point from the food source to the organism that eats it, showing how energy moves through the ecosystem.

25(c) Any three valid points: [3]

• The bird population would increase at first [1] because there are no hawks to hunt and eat them [1]
• As bird numbers increase, they would eat more caterpillars [1], so the caterpillar population would decrease
• Eventually, birds might face food shortage if caterpillars become scarce [1], leading to competition and possible decline

Alternative acceptable chain: More birds → less caterpillars → less food for birds → bird population drops → caterpillars recover, etc.

25(d) Any two valid effects with explanations: [4]

• Caterpillar population decreases sharply [1], so birds have less food and their population may also decrease [1]
• Grass population increases [1] because fewer caterpillars are eating it [1]
• Pesticide may poison the birds [1] if they eat caterpillars that have absorbed the chemical (biomagnification) [1]
• Hawk population decreases [1] due to fewer birds to eat / food chain disrupted [1]

Marking note: Each effect [1] with linked consequence/explanation [1]. Accept any reasonable ecological cascade effects.

MARK SCHEME SUMMARY

End of Answer Key